The present invention relates to a method and a device, particularly a battery management system, for determining an open-circuit voltage profile of a vehicle battery, dependent on a state of charge, in a vehicle.
Vehicle batteries for automotive applications are subject to ageing which changes the chemical and electrical properties of the vehicle battery. In this context, capacity and energy content are reduced whereas the inner resistance generally increases.
Particularly the open-circuit voltage of the vehicle battery is subject to ageing and changes the voltage profile thereof dependent on a state of charge in some vehicle batteries. This affects different algorithms which are carried out by means of a responsible battery management system. Said algorithms include, for example, determining the charging state and determining the capacity. In addition, the accuracy of said algorithms carried out by the responsible battery management system is reduced.
A measurement of the open-circuit voltage is possible by means of the GITT method (galvanostatic intermittent titration technique). To this end, a discharging and a charging of a battery are carried out with constant current. This measurement is advantageously performed when the current amplitude is as small as possible. The current amplitude can, for example, be selected according to a C-factor C20. That means that the current amplitude is selected in such a way that a discharging of a completely charged battery 20 lasts hours. As a result, the precision of the measurement increases with increasing measuring time.